feat(ui): add Rescan button to Edit Metadata dialog

Adds a Rescan button to the MetadataEditorModal footer that POSTs to the
new per-book rescan endpoint, with rescanning state (disabled + spinner,
matching the existing Mark Read pattern), success/error toasts, and a
page reload to pick up the refreshed cover and metadata.

templates/book_detail_modals.templ

@@ -609,7 +609,19 @@ templ MetadataEditorModal(book handlers.MediaDetail) {
 					</div>
 				</div>
 			</div>
-			<div class="flex justify-end space-x-3 p-6 border-t flex-shrink-0" style="border-color: var(--border);">
+		<div class="flex items-center justify-between p-6 border-t flex-shrink-0" style="border-color: var(--border);">
+			<button
+				@click="rescanBook()"
+				:disabled="rescanning"
+				class="btn btn-secondary"
+			>
+				<span x-show="!rescanning" class="inline-flex items-center gap-2">@Icon("sync", "h-4 w-4")<span>Rescan</span></span>
+				<svg x-show="rescanning" class="animate-spin inline-block h-5 w-5" viewBox="0 0 24 24" fill="none">
+					<circle class="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" stroke-width="4"></circle>
+					<path class="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4z"></path>
+				</svg>
+			</button>
+			<div class="flex space-x-3">
 				<button
 					@click="hideMetadataEditor()"
 					class="btn btn-secondary"
@@ -625,5 +637,6 @@ templ MetadataEditorModal(book handlers.MediaDetail) {
 				</button>
 			</div>
 		</div>
+		</div>
 	</div>
 }